Fire retardant compositions and methods and apparatuses for making the same

ABSTRACT

A method for forming yarn provides for forming an intermediate product being a fire retardant and heat resistant cohesive elongated network of fibers in a single operation by stretching and breaking filaments of a ribbon like tow starting material of longitudinally aligned filaments. The intermediate product may be wool-like with wavy and randomly oriented fibers formed by from the fragmented filaments. The single drafting operation includes directing the tow through first and second pairs of rollers, the second pair rotating faster than the first. The intermediate product may be spun directly into yarn in one spinning/twisting operation. The fire retardant and heat resistant yarn so produced may include 100% oxidized polyacrylonitrile fibers having an average length greater than about 15 cm. The yarn may be knitted or otherwise formed into fire-retardant and heat resistant fabrics or other products used in various applications.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority tocopending U.S. patent application Ser. No. 11/600,681, filed Nov. 15,2006, which claims priority to U.S. Provisional Patent Application Ser.No. 60/921,476, filed Nov. 16, 2005, the contents of which are hereinincorporated by reference in their entirety.

FIELD

The subject matter pertains to fire retardant compositions and methodsand apparatuses for making the same, and more particularly tocarbon-based fire retardant and heat resistant compositions, includingrovings, yarns, fabrics, and products made therefrom including but notlimited to coverings, upholstery, clothing, insulations, sleeves, ropes,barriers and masks, and textiles. The invention also relates to anintermediate product comprising, consisting essentially of, orconsisting of, a cohesive elongated network of fibers used to form yarn.The inventions also relates to methods and machines for producing fireretardant and heat resistant compositions and intermediates.

BACKGROUND

The following description includes information that may be useful inunderstanding the present invention. It is not an admission that any ofthe information provided herein is prior art, or relevant, to thepresently described or claimed invention, or that any publication ordocument that is specifically or implicitly identified is prior art or areference that may be used in evaluating patentability.

A fire retardant is a substance that helps to delay or preventcombustion. See Horrocks, A. R., Fire Retardant Materials (2001). Fireretardant clothing, for example, is widely used to protect persons whoare exposed to fire, particularly suddenly occurring and fast burningconflagrations. These include persons in diverse fields such as race cardrivers, military personnel and fire fighters, each of which may beexposed to deadly fires and extremely dangerous incendiary conditionswithout notice. For such persons, the primary line of defense againstsevere burns and even death is the protective clothing worn over some orall of the body.

Materials such as carbon fiber materials and aramid fiber materials havebeen used to form fire retardant materials for the manufacture ofclothing. Carbon fibers are typically in the form of long bundles oflinked graphite plates that form a crystal structure lying parallel tothe fiber axis. Carbon fibers are anisotropic and their elastic modulusis higher in the direction of the axis than it is in other directions.In other words, the individual fibers can withstand pulling, i.e., theycan stretch before breaking, in the axial direction to a greater extentthan they can withstand bending at an angle to the axis or lateralstretching. Most carbon fiber materials are made from thousands ofindividual filaments and include thousands of fibers.

Carbon fiber materials have advantageous mechanical, physical andchemical properties. In addition to being nonflammable, they are light,stiff and strong. The strength of a carbon fiber is comparable to thatof steels and the stiffness of carbon fibers is generally greater thanmetal, ceramic or polymer-based materials. Carbon fibers have otherdesirable properties such as excellent corrosion and fatigue resistanceand dimensional stability. Carbon fibers and their composites aretherefore well suited for applications in which chemical inertness,strength, stiffness, lightness, and fatigue resistance are importantrequirements. For example, in the aerospace and defense industries,materials made of carbon fibers have been increasingly used both in theinterior of aircrafts as flame resistant materials and as criticalstructural components to increase fuel efficiency and enhance structuralstrength.

Carbon fibers may be produced from a variety of precursor materials.Among these precursor materials are polyacrylonitrile (PAN), petroleumor coal tar pitch and certain phenolic fibers. Cellulosic fibers such asrayon and cotton may also be used as additives. Different precursormaterials produce carbon fibers with different morphologies anddifferent specific characteristics. PAN-based carbon fiber materialsexhibit superior tensile strength, are comparatively low in cost, andare well suited for use in the construction of consumer goods such assporting goods and high-performance apparel.

Various methods are known for producing carbon fibers from variousprecursor materials. Such methods include pyrolytic processes andpyrolysis. It is well established that the mechanical properties ofcarbon fibers are improved by increasing their crystallinity and themolecular order within the fiber. One way to increase crystallinity andstructural order is through a process of stabilization and carbonizationthrough tension. One common pyrolysis reaction is an oxidativestabilization process in which a carbon fiber is treated at about200-300.degree. C. under tension in an oxidizing environment. During theprocess, oxygen, nitrogen and/or hydrogen is removed from the fiber,resulting in an increase of carbon content in the fiber. In addition topreventing fiber shrinkage, the tension applied during this processmaintains the molecular orientation and order of the fiber, which inturn increases the tensile strength of the stabilized fiber.

During pyrolysis of PAN, the oxidation and stabilization inducesintramolecular cyclization of the oriented molecules with the release ofmost of the hydrogen and part of the nitrogen from the fibers. Theresulting PAN polymers are called “oxidized PAN” and oxidized PANtypically has a carbon content of about 55-68% and a density of about1.30 to 1.50 g/cm.sup.3. Oxidized PAN fibers have several advantages asflame resistant materials. Oxidized PAN fibers exhibit excellent heatinsulation properties and low thermal conductivity. Oxidized PAN fibersalso have a high limiting oxygen index (LOI), typically between 40-60%oxygen making them more flame resistant than many other organic fibers.Moreover, textiles that include strands of oxidized PAN fibers, unlikeother flame resistant organic fibers, retain their appearance andtextile characteristics after open flame exposure. Oxidized PAN fibersare electrically nonconductive and function as effective electricalinsulators even after exposure to heat and open flames. Oxidized PANfibers also exhibit excellent chemical resistance to organic solventsand most acids and bases. Moreover, oxidized PAN fiber strands aresofter, more pliable and malleable than strands of pure carbon fibers.As such, oxidized PAN fiber strands are well suited for use in compositeheat resistant thermal insulations and textiles for high technologyapplications, and have been used in composite fire blocking fabrics forseating in the aerospace and automobile industries and in themanufacture of composite fire retardant and protective clothing forpeople exposed to the danger of an open flame.

Currently, there are at least three types of oxidized PAN materialsavailable commercially: staple fibers, large filament tow materials, andsmall filament tow materials. In using these materials in the productionof composite industrial and consumer products, the staple fibers andlarge filament tow materials are often spun into yarn using complex,multi-step processes that commonly include, for example, the addition ofstrengthening fibers to the carbon fiber material precursor, or theaddition of laminate coatings to fabrics that they are used to prepare.

For staple fibers, relatively short natural or synthetic fibers, thefirst step in the production of yarn is “carding”, in which the fibersare opened and combed over cylinders that contain extremely fine wiresor aligned teeth. The fibers are then aligned in one direction to form alarge loosely assembled but not twisted continuous strands of fibersknown as “sliver”. Several strands of sliver are then drawn multipletimes onto drawing frames to further align the fibers to improveuniformity as well as to reduce the diameter of the sliver. The drawnsliver is then fed into a roving frame to produce “roving” by furtherreducing the diameter and imparting a slight false twist. Finally, theroving is fed into a spinning (i.e., winding and/or twisting) framewhere it is spun into yarn.

For large filament tow, the first step is different, and consists of astretch-breaking process in which the large tow is broken into multiplefragments and aligned into sliver. The sliver is then further processedas described above. These processes are laborious, inefficient andcostly, require as many as 6 or 8-12 separate steps and often requirethe use of more than one type of apparatus.

It would be desirable to provide an economical process for convertingoxidized PAN materials or other starting materials into yarn using areduced and minimum number of operations. It would be further desirableto provide a process for converting oxidized PAN materials or otherstarting materials into yarn using a single apparatus.

Oxidized PAN materials provide superior fire retardant and heatresistant qualities, i.e., a high LOI and superior Thermal ProtectivePerformance, TPP, but when they are formed according to conventionalmethods, the strands formed from oxidized PAN carbon fibers aretypically brittle, weak and prone to abrasion and cutting. Yarns formedfrom pure oxidized PAN using conventional methods exhibit undesirablylow cut resistance, abrasion resistance and tensile strength and do notinclude sufficient tensile strength to be knit or woven into fabrics. Assuch, fabrics made from oxidized PAN carbon fiber strands usingconventional methods typically include the fire retardant and heatresistant oxidized PAN strands in combination with one or more highstrength or strengthening filaments/fibers. Aramid fiber is an exampleof such a strengthening filament. The strengthening filaments/fibers incombination with the oxidized PAN produces a fibrous blend havingimproved tensile strength, cut resistance and durability but theadditives, i.e., the strengthening fibers, compromise the flameretarding and heat resisting properties of the fabric.

It would be desirable to produce a yarn and textile and other materialsthat are composed entirely of oxidized polyacrylonitrile fibers orcarbonized polyacrylonitrile fibers yet exhibit sufficient tensilestrength to be knittable. It would also be desirable to manufacture anintermediate product that may be used to produce such yarns and textileand other materials.

BRIEF SUMMARY

The inventions described and claimed herein have many attributes andembodiments including, but not limited to, those set forth or describedor referenced in this brief summary. The inventions described andclaimed herein are not limited to or by the features or embodimentsidentified in this brief summary, which is included for purposes ofillustration only and not restriction.

To address the aforementioned and other needs, and in view of itspurposes, the present invention provides, in one aspect, a fireretardant and heat resistant yarn including 100% polyacrylonitrile (PAN)fibers. In one embodiment, the fibers have an average length greaterthan about 10 cm. In another exemplary embodiment, the fibers have anaverage length greater than about 15 cm. In another embodiment thefibers have a length within a range of about 2.5 cm to about 23 cm. Inanother embodiment the PAN fibers may have a length within a range ofabout 15 cm to about 23 cm. In one embodiment the PAN is oxidized PAN.In another embodiment the PAN is carbonized PAN.

In another aspect, the present invention provides a textile made from afabric consisting essentially of or consisting of yarn formed of aplurality of fire retardant and heat resistant fibers and nostrengthening fibers, each of the fire retardant and heat resistantfibers comprising 100% polyacrylonitrile (PAN). In one embodiment,substantially all of the fibers have an average length greater thanabout 10 or 15 cm. In another embodiment the fibers have a length withina range of about 2.5 cm to about 23 cm. In another embodiment the PANfibers may have a length within a range of about 15 cm to about 23 cm.In one embodiment the PAN is oxidized PAN. In another embodiment the PANis carbonized PAN.

In another aspect, the present invention provides a fire retardant andheat resistant yarn comprising 100% carbonized polyacrylonitrile (PAN)fibers, the fibers having an average length greater than about 10 or 15cm, substantially all of the fibers having a length within a range ofabout 2.5 cm to about 23 cm.

In another aspect, the present invention provides a fire retardant andheat resistant yarn comprising 100% oxidized polyacrylonitrile (PAN)fibers, the fibers having an average length greater than about 10 or 15cm, most or all of the fibers having a length within a range of about2.5 cm to about 23 cm.

In another aspect, the present invention provides a method for producinga cohesive elongated network of fibers. The method includes providing astarting material comprising a tow of filaments forming a ribbon anddrawing the starting material through a first pair of rollers and asecond downstream pair of rollers of a drafting component, the secondpair of rollers having a second rotational speed that is faster than afirst rotational speed of the first pair of rollers, thereby stretchingand breaking the filaments of the tow of filaments to form a cohesiveelongated network of fibers formed by stretching and breaking thefilaments. In one embodiment the starting material is oxidized PAN. Inanother embodiment the starting material is carbonized PAN.

In another aspect, the present invention provides a method for producinga fire retardant and heat resistant cohesive elongated network offibers, the method including providing a starting material comprising aplurality of longitudinally aligned filaments with limited twists, andconverting the starting material into the fire retardant and heatresistant cohesive elongated network of fibers in a single operationthat stretches and breaks the filaments of the starting material,thereby separating at least some of the filaments into a plurality ofthe fibers having lengths shorter than the corresponding filaments fromwhich the fibers were separated. In one embodiment the starting materialis oxidized PAN.

In another aspect, the present invention provides a method for producingyarn. The method comprises providing a ribbon comprising a tow offilaments on a spool on an apparatus, pulling the ribbon from the spoolby unwinding and feeding the ribbon to a drafting component, stretchingand breaking the filaments of the tow of filaments to form a cohesiveelongated network of fibers in a single operation by directing thestarting material through first and second pairs of rollers of adrafting component while applying pressure to the first and second pairsof rollers, the first pair of rollers having substantially conterminousopposed surfaces and spinning at a first speed and the second pair ofrollers being downstream and having substantially conterminous opposedsurfaces and spinning at a second, faster speed, the pressure urging thesecond pair of rollers toward each other and the first pair of rollerstoward each other, and spinning and twisting the cohesive elongatednetwork of fibers onto a bobbin thereby forming yarn, in a singleoperation. The pulling, stretching and breaking and spinning andtwisting operations all take place in the apparatus. In one embodimentthe ribbon of tow of filaments is oxidized PAN and the spool is on atension disk such that the tow is flat and untwisted when fed to thedrafting component.

In another aspect, the present invention provides an apparatus forconverting a ribbon of tow comprising a plurality of longitudinallyaligned filaments into a cohesive elongated network of fibers capable ofbeing directly spun into yarn. The apparatus comprises a first pair ofsubstantially conterminous rollers having a first rotational speed andreceiving the ribbon of tow therebetween, a second pair of substantiallyconterminous rollers downstream from the first pair of rollers having asecond rotational speed greater than the first rotational speed therebystretching and breaking the plurality of longitudinally alignedfilaments to form the cohesive elongated network of fibers consisting ofa collection of randomly oriented fibers formed by breaking thefilaments. A pressurizing element applies pressure that urges the firstpair of rollers toward each other and the second pair of rollers towardeach other. In one embodiment the tow is oxidized PAN.

In another aspect, the present invention provides a fire retardant andheat resistant strand of material comprising 100% oxidizedpolyacrylonitrile (PAN) fibers and formed according to the method ofproviding a starting material comprising a tow of filaments forming aribbon and drawing the starting material through a first pair of rollersand a second downstream pair of rollers of a drafting component whileurging the first pair of rollers toward each other and/or the secondpair of rollers toward each other, the second pair of rollers having asecond rotational speed that is faster than a first rotational speed ofthe first pair of rollers, thereby stretching and breaking the filamentsof the tow of filaments to form a cohesive elongated network of fibersformed by stretching and breaking the filaments.

In another aspect, the present invention provides a fire retardant andheat resistant yarn comprising 100% oxidized polyacrylonitrile (PAN)fibers and formed according to the method of providing a startingmaterial comprising a plurality of longitudinally aligned oxidized PANfilaments with limited twists, converting the starting material into afire retardant and heat resistant cohesive elongated network of fibersin a single operation that stretches and breaks the filaments of thestarting material, thereby separating at least some of the filamentsinto a plurality of the fibers having lengths shorter than thecorresponding filaments from which the fibers were separated. Thecohesive elongated network of fibers is directly spun into yarn in onespinning step that further twists the cohesive elongated network offibers.

According to yet another aspect, the present invention provides, in amethod for forming yarn from a tow material, the improvement comprisingproviding the tow material in ribbon form, converting the tow materialto a cohesive elongated network of fibers in a single operation thatstretches and breaks filaments of the tow material into the fibers, andspinning and twisting the cohesive elongated network of fibers into yarnin one further step. In one embodiment the tow material is oxidized PAN.

BRIEF DESCRIPTION OF THE DRAWING

Aspects of the present inventions are also described in light of theaccompanying drawings. It is emphasized that, according to commonpractice, the various features of the drawings are not necessarily toscale. On the contrary, the dimensions of the various features arearbitrarily expanded or reduced for clarity. Like numerals denote likefeatures throughout the specification and drawings.

FIG. 1 illustrates the chemical structures of polyacrylonitrile (PAN),oxidized PAN and carbonized PAN.

FIG. 2 illustrates one embodiment of an apparatus used to carry out amethod of the invention;

FIG. 3A illustrates a spool of small filament tow oxidized PAN, oneembodiment of a starting material that may be used according to theinvention and FIG. 3B illustrates an exemplary tension disk upon whichthe starting material may be provided;

FIG. 4 is an expanded, cross sectional view of the drafting component ofthe apparatus shown in FIG. 2;

FIG. 5 depicts the feeding, drafting, twisting and winding components ofthe apparatus shown in FIG. 2; and

FIG. 6A is a cross sectional, perspective view of a small filament towstarting material in ribbon form; FIG. 6B is a cross sectional andperspective view of the cohesive elongated network of fibers formed fromthe starting material shown in FIG. 6A according to the invention; and

FIG. 6C is a side, cross sectional view of the cohesive elongatednetwork of fibers shown in FIG. 6B.

DETAILED DESCRIPTION

The invention includes the production of a cohesive elongated network offibers that can serve as intermediates for the production of goods toimpart enhanced performance characteristics such as strength, fireretardance and heat resistance. A cohesive elongated network of fibersintermediate may include a plurality of fibers of one or more types ofmaterials, wherein the fibers are formed from longer filaments and arerandomly associated in the network in a wool-like configuration. Thecohesive elongated network of fibers is typically a continuous mass andmay be directly spun into yarn in one further spinning operation. Theinvention also relates to the yarn made therefrom.

The invention also provides a two-step process for converting towstarting material into yarn in a single apparatus. The invention furtherrelates to an apparatus for feeding and drafting fibers to produce thecohesive elongated network of fibers.

The present invention also provides carbon-based fabrics made from theprocesses, inventive yarns and intermediates of the invention, as wellas goods made therefrom. The goods may be textile fabrics, for example,consisting essentially of yarn formed of a plurality of fire retardantand heat resistant fibers and no strengthening fibers. Each of the fireretardant and heat resistant fibers may be 100% polyacrylonitrile (PAN).The fibers may include an average length greater than about 10 cm, mostor all of the fibers having a length within a ran ge of about 2.5 cm toabout 23 cm or from about 15-23 cm. In another embodiment, the majorityof fibers have an average length greater than about 15 cm. The PAN maybe oxidized PAN, carbonized PAN or other suitable materials. In additionto textiles, goods made from the carbon-based fire retardant and heatresistant compositions of the invention, in addition to rovings, yarns,and fabrics, include but are not limited to coverings, upholstery,clothing, insulations, sleeves, ropes, and barriers and masks.

DEFINITIONS

The term “filament” refers to a single strand of fibrous material, whichmay be part of an organized or random collection of filaments. As usedin the specification and appended claims, filament refers to a single,continuous or discontinuous elongated strand formed from one or moremetals, ceramics, polymers or other materials and that has no discretesub-structures (such as individual fibers that make up a “thread”).Filaments can be formed by extrusion, molding, melt-spinning, filmcutting, or other known filament-forming processes. A “filament” differsfrom a “thread” in that a filament is, in essence, one continuous strandrather than a plurality of fibers or strands that have been carded orotherwise joined together to form a thread. “Filaments” arecharacterized as strands that are long and continuous, and may be aslong as the entire length of yarn (i.e. a monofilament).

The terms “fiber” and “fibers”, as used in the specification andappended claims, refer to any slender, elongated structure that can becarded or otherwise formed into a thread. Fibers may be truncatedfilaments and may be formed by the separation of filaments into shortercomponents. Fibers are therefore characterized as being shorter than thefilaments from which they may be formed. Examples include “staplefibers”, a term that is well-known in the textile art. The term “fiber”differs from the term “filament”, which is defined separately above.

The term “thread”, as used in the specification and appended claims,refers to continuous or discontinuous elongated strands formed bycarding or otherwise joining together one or more different kinds offibers. The term “thread” differs from the term “filament”, which isdefined separately herein.

The term “yarn”, as used in the specification and appended claims,refers to an assemblage of strands. “Threads” and “filaments” are bothexamples of “strands” which is used rather generally as an elongatedfibrous member. Yarn has a virtually continuous length that is suitablefor use in knitting and/or weaving, either alone or with other filamentsor yarns, into textile materials.

The term “cohesive elongated network of fibers” refers to a continuousmass of a randomly arranged collection of untwisted fibers that are heldtogether by mechanical, physical and noncovalent chemical forces.

The term “wool-like” refers to a filament or fiber network in which therandom collection of untwisted filaments or fibers includes individualfilaments or fibers that are partially or completely crinkled, curled,crimped, wavy and/or otherwise curved.

The term “fabric”, as used in the specification and appended claims,refers to an artifact made by weaving, felting, knitting, crocheting orotherwise assembling one or more different types of yarns into a desiredlayer.

The term “limited twist”, as used in the specification and appendedclaims, refers to filaments or fibers having a twist number less than 50per meter.

The term “PAN” refers polyacrylonitrile. See FIG. 1. The term “oxidizedPAN” refers to polyacrylonitrile fiber which has been oxidativelystabilized. See FIG. 1. Oxidized PAN can also be further processed toform carbonized PAN. See FIG. 1.

The term “carbon fiber” refers to a fiber containing at least about 90%carbon, which is usually obtained by the controlled pyrolysis ofappropriate fibers.

The term “tow” refers to a collection of untwisted continuous filamentsand is often referred to in terms of the number of filaments in thecollection, such as 3K, 6K, etc. “Small filament tow” may generallydescribe tow having about 24K filaments or less.

The term “LOI” refers to the limiting oxygen index, which is a measureof the percentage of oxygen that has to be present to support combustionof a material. The higher the LOI, the lower the flammability.

The meaning of other terminology used herein should be easily understoodby someone of ordinary skill in the art.

The present invention provides a simple, efficient and cost-effectivemethod to draft various filamentous starting materials into wool-likefiber networks. A typical filamentous starting material has straight,long filaments with very limited inter- and intra-filament twisting. Thefilaments of the starting material may be well organized and alignedlongitudinally (i.e., they are generally parallel to one another) andmay come in the form a of a ribbon or in other forms. Exemplaryfilamentous starting materials include, without limitation, PAN,oxidized PAN, polyester materials, aramid materials, nylon materials,rayon materials, and metal materials such as stainless steel, nickel,and various alloy materials. In various exemplary embodiments, thestarting materials may represent a filamentous starting material orfibers.

Typical starting or precursor materials are filament tows consisting ofuntwisted parallel filaments of a uniform length equal to the length ofthe tow. Preferably, these precursor tows may have a twist number lessthan 50 per meter (“limited twist”) and each filament has a length of noless than 2 meters. More preferably, the precursors may include a twistnumber less than 25 per meter. Yet more preferably, the precursors mayhave a twist number less than 10 per meter, or less than 5 per meter.For polymeric filaments, each filament may advantageously have a decitex(1 g/10,000 meters) of no greater than 67 and the total measure of thetow is no greater than 32,000 decitex. For stainless steel, eachfilament may advantageously have a decitex of no greater than 550 andthe total measure of the tow may be no more than 260,000 decitex.

In one embodiment, the starting material may be oxidized PAN tow with nogreater than 192K filaments and a filament diameter of no greater thanabout 50 micrometers but other sizes of tow and other filament diametersmay be used in other exemplary embodiments. Preferably, the oxidized PANhas a tow of no greater than about 96K, and a filament diameter of nogreater than about 25 micrometers. More preferably, the oxidized PAN hasa tow of no greater than about 48K. Yet more preferably, the oxidizedPAN has a tow of no greater than about 24K and may include a tow ofabout 3K to about 12K. Oxidized PAN tow is commercially available from anumber of different companies, such as Asahi Chemical Industry Co., Ltd.at Osaka, Japan (LASTAN®), Zoltek at St. Louis, Mo. (PYRON®), SGL CarbonAG at Wiesbaden, Germany (PANOX®), Dow Chemical Company at Midland,Mich. (CURLON®), and a small filament tow supplied by J. D. Seal andGasket Company of China. However, the present invention is not limitedby the source of oxidized PAN tow. In addition, many publications areavailable with sufficient information to allow one to manufactureoxidized PAN tow with desired structures and properties.

The present invention is also not limited by the chemical composition ofoxidized PAN, which is a function of the composition of the PANprecursor, and the oxidative stabilization process to convert PAN intooxidized PAN. The PAN precursor can be, for example, a homopolymer ofacrylonitrile, acrylonitrile based copolymers, and acrylonitrile basedterpolymers. The copolymers may preferably contain at least about 85%(by mole) of acrylonitrile monomers and up to about 15% (by mole) of oneor more mono-vinyl units. Exemplary other vinyl monomers that are ableto copolymerized with acrylonitrile include methacrylic acid esters andacrylic acid esters such as methyl methacrylate, ethyl methacrylate,propyl methacrylate, butyl methacrylate, methyl acrylate and ethylacrylate; vinyl esters such as vinyl acetate and vinyl propionate;acrylic acid, methacrylic acid, maleic acid, itaconic acid and saltsthereof; vinylsulfonic acid and the salt thereof.

Oxidized PAN (see FIG. 1) that is useful in the practice of the presentinvention can be produced from various PAN materials using wellestablished oxidative pyrolytic processes. Oxidative stabilization maybe performed at atmospheric pressure in the presence of oxygen at atemperature of about 200-300.degree. C. The chemical composition ofoxidized PAN is affected by the duration of time and the temperature ofthe oxidation process. In one aspect, the oxidized PAN used in thepractice of the present invention may have a density of about 1.30 toabout 1.50 g/cm.sup.3, a carbon content of about 55 to about 68%, and an“LOI” (Limiting Oxygen Index) value of about 40 to about 60%. In anotherembodiment, the starting material may be carbonized PAN (see FIG. 1)which is oxidized PAN that has been further processed through acarbonization and graphitization processes as described below. In stillanother embodiment, the starting material may be activated PAN asdescribed below.

In another embodiment, the starting material may be polyester with a towof no greater than 192K and a filament diameter of no greater than 50micrometers although other diameters and numbers of filaments may beused in other exemplary embodiments. The tow of polyester filaments mayadvantageously have no greater than 96K filaments and the filamentdiameter may be no greater than 25 micrometers. More preferably, thepolyester tow may be a tow of no greater than 48K. Yet more preferably,the polyester tow may have no greater than 24K filaments. Yet morepreferably, the polyester tow may have no greater than 12K filaments.

In yet another embodiment, the starting material may be stainless steelwith a tow of no greater than 192K and a filament diameter of no greaterthan 50 micrometers. Preferably, the precursor filamentous material hasa tow of about no greater than 96K filaments, the filaments havingdiameters no greater than 20 micrometers. More preferably, the stainlesssteel material has a tow of no greater than 48K. Yet more preferably,the stainless steel material has a tow of no greater than 24K. Yet morepreferably, the stainless steel tow is a tow of no greater than 12K.

In yet another embodiment, the starting material is an aramid materialwith a tow of no greater than 192K and a filament diameter of no greaterthan 50 micrometers. The precursor may advantageously have a tow of nogreater than 96K with filaments having diameters no greater than 20micrometers. More preferably, the filamentous aramid starting materialhas a tow of no greater than 48K. Yet more preferably, the aramidmaterial may have a tow of no greater than 24K. Yet more preferably, thearamid material may have a tow of no greater than 12K. An aramidmaterial is an aromatic polyamide and comes with many different gradesand properties for various applications. The aramid fiber has excellentenvironmental and thermal stability, static and dynamic fatigueresistance, and impact resistance. Aramid filaments have the highestspecific tensile strength of any commercially available continuousfilament tow. Examples of aramid materials include, but are not limitedto, KEVLAR® by DuPont (Greenville, Del.), TWARON® and TECHNORA® byTeijin (Arnhem, Netherlands).

The methods and apparatuses of the present invention can be used todraft two or more strands of fibers simultaneously. When the fibersdrafted are of different types, a blended fiber network is obtained.Other fibers that may be used include linear fibers that may be selectedfrom natural or synthetic fibers. Exemplary fibers include carbonfibers, ceramic fibers, glass fibers, metal fibers, carbonaceous fibers(e.g. cotton, wool, polyester, polyolefin, nylon, rayon or novoloidphenolic), inorganic fibers (e.g. silica, silica alumina, potassiumtitanate, silicon carbide, silicon nitride, boron nitride, and boron),acrylic fibers, tetrafluoroethylene fibers, polyamide fibers, vinylfibers, protein fibers, and oxide fibers derived from boron, thoria orzirconia.

Processing/Apparatus

In one aspect of the present invention, the apparatus of the presentinvention comprises feeding and drafting components and a spinningcomponent. The feeding process involves feeding a continuous precursorof filamentous material into the drafting mechanism. The feeding processis passive and advantageously maintains the fiber in a flatconfiguration, with minimum twist, i.e. no more than double the twist ofthe starting material.

The feeding component may be a conventional “ring spinning frame”.However, other conventional feeding components and methods may also beappropriate. Furthermore, the feeding component may comprise two or morefeeding elements so that two or more strands of fibrous or filamentousstarting materials may be drafted simultaneously. When the fibrous orfilamentous starting materials fed into the drafting component are ofdifferent types, a blended fibrous network is produced.

FIG. 2 illustrates one apparatus 1 having feeding component 9, draftingcomponent 11 and spinning component 13. The illustrated exemplaryapparatus is a dual-mode, i.e. side-by-side apparatus that is capable offorming two yarns, one on the left hand side and one on the right handside in the illustrated embodiment. Feeding component 9 has four rollersor posts in the illustrated embodiment: 3 a, 3 b, 5 a and 5 b. Startingmaterial 7 is placed on each of rollers 3 a, 3 b, 5 a and 5 b. Thestarting material 7 on the different rollers may be the same ordifferent.

In one embodiment, starting material 7 may be small filament tow inribbon form such as shown in FIG. 3A. The small filament tow startingmaterial 7 may be disposed on spool 8, may consist of untwisted smallfilament tow consisting of 3K, 6K, 12K or 24K filaments and mayadvantageously be oxidized PAN.

Referring to FIGS. 2 and 3, within feeding component 9, startingmaterial 7 is unwound from the respective roller 3 a, 3 b, 5 a or 5 band fed as feed material 15 to drafting component 11. According to oneembodiment, feed material 15 may be untwisted small filament towconsisting of 3K, 6K, 12K or 24K filaments. In one embodiment, startingmaterial 7 and the small filament tow feed material 15 may be oxidizedpolyacrylonitrile (PAN). According to some exemplary embodiments,rollers 3 a, 3 b, 5 a and 5 b may include tension disks (see FIG. 3B)that maintain tension on feed material 15 and enable feed material 15 tobe delivered to drafting component 11 in a flat and untwisted manner.Various suitable tension settings may be used. In one exemplaryembodiment, the tension and feeding component may enable the feedmaterial to be maintained essentially flat and untwisted for a length ofup to about 30 meters between the rollers 3 a, 3 b, 5 a or 5 b anddrafting component 11. Various arrangements may be used for unwindingstarting material 7 from spools 8 in various directions andorientations. FIG. 3B shows an exemplary starting material 7 on spool 8mounted on tension disk 10 of feeding, component 9. Further details ofstarting material 7/feed material 15 will be shown in FIG. 6A.

Feed material 15 enters drafting component 11 and is fed through asystem of pairs of rollers including first roller pair 17, second rollerpair 19 and third roller pair 21. The tension applied to feed material15 advantageously maintains feed material 15 untwisted and flat suchthat it enters drafting component 11 such that the plane of feedmaterial 15 is parallel to the plane formed by the tangent to therollers, i.e., the opposed sides of the ribbon of tow may be flushagainst each of the pair of rollers in exemplary embodiments. Pendulumcarrier 23 includes a pendulum and applies pressure urging each ofroller pairs 17, 19 and 21 toward each other. In an exemplaryembodiment, the opposed surfaces of each of the rollers of a pair ofrollers, are conterminous so that the material passing between the pairof rollers is firmly gripped by the pair of rollers. A more detaileddepiction of drafting component 11 is provided in FIG. 4. In anotherexemplary embodiment, drafting component 11 may consist of only twopairs of rollers. Apparatus 1 illustrated in FIG. 2 is intended to beexemplary only and in other embodiments, more of fewer feedingcomponents, each with at least two pairs of rollers, may be included.

The drafting process that takes place in drafting component 11 stretchesand breaks some or all of the longitudinally-aligned filaments of theribbon-like small filament tow feed material 15 and in one draftingoperation, converts the ribbon-like small filament tow feed material 15to a cohesive elongated network of fibers consisting of a pluralityfibers produced by separating the long incoming filaments into aplurality of shortened fibers as each successive pair of downstreamrollers rotates, i.e., turns or spins at a faster rotational speed thanthe immediately upstream pair of rollers thus pulling, stretching andbreaking the filaments of the tow starting material. The produced fibersmay have lengths ranging from about 2-9 inches in one embodiment butother ranges of lengths may be obtained ion other exemplary embodiments.In one exemplary embodiment, the average fiber length may be greaterthan 15 centimeters. In another exemplary embodiment, the average fiberlength may be greater than 10 cm. In one exemplary embodiment, most orall of the fibers may include a length of greater than 15 centimeters.The average and minimum length and range of fiber lengths is determinedby the draft ratio between the rollers and the size of the tow andfilament diameter of feed material 15. The term “draft ratio” refers tothe ratio of the speed of one pair of rollers to the speed of thepreceding pair of rollers of a drafting component. In an advantageousembodiment, the rollers of each pair of rollers may be arranged suchthat the axes of the rollers (shown as the intersections of the “X′s” inFIG. 4), are parallel to each other. This parallel alignment is alsodepicted in FIG. 5 by the dashed line between rollers. In oneembodiment, the axes of each pair of rollers, e.g., first roller pair17, may also be parallel to each other as depicted by the dotted linebetween third roller pair 21 shown in FIG. 5.

During the drafting process, each roller of a pair applies an equal andopposite pressure onto opposing sides of feed material 15 so that feedmaterial 15 can only be moved by the rotation of the rollers and doesnot slip away from the rollers. Each of the pairs of rollers 17, 19 and21 may advantageously be conterminous or substantially conterminous attheir contact points. Stated alternatively, in one exemplary embodiment,the rollers may be conterminous at a contact point and in anotherexemplary embodiment they may be substantially conterminous, i.e., inclose proximity and separated by a small distance equal to or less thatthe dimension of feed material 15 or contacting in areas except wherefeed material 15 passes therebetween. The pressure or other forceapplied onto each pair of rollers may be accomplished by varioussuitable conventional methods and may be applied either independently,i.e., separately, or cooperatively as in the illustrated embodiment. Inone exemplary embodiment, a weight element may be used to exertappropriate pressure onto the rollers. The pressure can be generated byapplying the weight element onto at least one of the rollers of eachpair. In the illustrated embodiment, and to simplify the design of theapparatus of the present invention, the weight element is applied toonly one of the two rollers of each pair but in other exemplaryembodiments, other configurations may be used.

In the illustrated embodiment, such as shown in FIGS. 2 and 4, a singleweight element-pendulum carrier 23 cooperatively exerts appropriatepressure onto one roller of each pair of rollers 17, 19 and 21 so thatthe rollers of the roller pair are urged toward each other and the towmaterial is moved by the rotation of the mechanically-driven rollers. Inone embodiment such as illustrated in FIG. 2, one roller from the first17 and second pairs of rollers is attached to pendulum carrier 23. Thethird pair of rollers 21 is attached to the frame of apparatus 1. Thisarrangement is exemplary only and other arrangements may be used inother exemplary embodiments. The pressure is adjustable by adjusting theweight of pendulum carrier 23 and by varying the relative position of apendulum or other members on pendulum carrier 23, and the rollers. Thependulum carrier is preferably detachable from the drafting component 11or may swing open on a hinge for easy access to the rollers. Mechanicalrotation of the rollers may be accomplished by any suitable andconventional manual or automatic method.

The rollers can be made from a variety of materials including, butwithout limitation, rubber, metal such as steel and aluminum, wood,polymer resins and composite material such as fiberglass. Rollersattached to apparatus 1 may include an uneven surface 31 or “teeth,”i.e., any uneven surface of any configuration including ridges,striations, individual protrusions, etc., and may be drivenmechanically. As such, at least one of the rollers may be metal in anexemplary embodiment. According to the embodiment in which the surface31 of the roller includes teeth, the teeth can have several differentconfigurations such as the alignment of teeth being parallel to the axisof the roller or forming an angle relative to the axis of the roller.The teeth may be evenly distributed on surface 31 of the roller forconsistency of the quality of the filament network produced. The rollersattached to pendulum carrier 23 (one roller from each of first 17 andsecond pair 19) may be mechanically driven or may be slave rollers whichare driven by the corresponding roller attached to the apparatus 1. Somerollers such as the rollers attached to pendulum carrier 23 may includeoutside coverings or cots 33 formed of materials such as rubbers,plastics, polymers, natural polymers, cotton, ceramics, metals andalloys. In one embodiment, cot 33 may be rubber and include a hardnessof about 50 to 90 or about 65-90 according to the Shore A hardnessscale. In one embodiment, the rubber cot may include a hardness of about75 according to the Shore A hardness scale.

Referring to FIG. 4, distance 26 between first pair of rollers 17 andsecond pair of rollers 19 may be about 105 mm in one embodiment but mayrange from about 50 to about 200 mm in other exemplary embodiments.Distance 28 between third pair of rollers 21 and second pair of rollers19 may be about 135 mm in one exemplary embodiment but may range fromabout 50 to about 200 mm in other exemplary embodiments. Distance 30between first pair of rollers 17 and third pair of rollers 21 may beabout 240 mm in one embodiment and about 180 mm in another embodimentbut may be about 150 mm or greater in other exemplary embodiments.

In another embodiment, drafting component 11 may have three or morepairs of rollers. In one aspect, the drafting component has no greaterthan ten pairs of rollers. In another aspect, the drafting component mayhave three to six pairs of rollers. In one particular embodiment, thedrafting component has two pairs of rollers. As depicted in FIGS. 2, 4,and 5, the arrangement of rollers is such that the feed material 15first contacts first roller pair 17, then passes through the secondroller pair 19, and comes out of third roller pair 21 as a stretchedmaterial or a frayed ribbon (see FIGS. 6A-6C) for further drafting or asa fluffy fibrous network intermediate. The three pairs of rollers canhave a variety of arrangements within the drafting component. Onearrangement for the three pairs of rollers is illustrated in FIG. 5.Similar to the other two pairs, the rollers of the second roller pair 19are so arranged that their axes are parallel to each other. Optionally,the axes of the second rollers may also be parallel to one of the othertwo roller pairs or both. Similar to the drafting component describedabove, one roller from each roller pair 17, 19, 21 may be attached topendulum carrier 23 with the other roller of each roller pair 17, 19, 21attached to apparatus 1. Second roller pair 19 may be removable from theapparatus so that the drafting component can easily be transformed intoa drafting component with two pairs of rollers as described above andvice verse. The pressure exerted onto each pair of rollers is adjustedby the weight of pendulum carrier 23 and by varying the relativeposition of pendulums on the pendulum carrier 23 with respect to therollers. The three rollers attached to the apparatus may be metalrollers with teeth and driven mechanically whereas the other three areslave rollers and driven by its counterpart. The teeth on the surface ofthe roller can have several different arrangements as described above.The three rollers on the pendulum carrier may advantageously includecots 33 as described above.

Essentially, drafting component 11 stretches and/or breaks andrandomizes the long filaments of the ribbon-like small filament towincoming material to form a wool-like network, i.e., a cohesive andcontinuous fibrous network formed of a plurality of wavy fibers formedwhen the longer filaments are stretched and broken and separated intothe smaller fibers.

Drafting is accomplished by a stretching force created due to thedifference in speed between pairs of rollers, wherein at least onedownstream pair of rollers operates at a greater speed than the closestupstream pair of rollers. The draft ratio may range from about 1.1 toabout 50 in various embodiments but other draft ratios may be usedalternatively. In an exemplary embodiment, the draft ratio may liewithin a range of about 6 to 29. The pressure urging the rollerstogether is adjusted according to the type of feed fiber and thedrafting ratio. The pressure on the rollers can be same or different andmay be accomplished using different pendulum weights. By varying thespeed difference and the pressure exerted by the pendulum, the apparatusis able to process different fibers with various tows, and producecohesive fibrous networks with various characteristics, such asdifferent average fiber lengths and diameters, e.g., a plurality oflongitudinally aligned filaments may be collectively separated into afiber consisting of more than one filament.

Typically, the rotational speed of the downstream pair of rollers isslightly faster than that of the preceding pair of rollers so that asmall force is exerted on the feed material. This force may be used tostraighten the filamentous material being drafted, for effectivedrafting. Sometimes, the incorporation of the second rollers alsoenhances the stability of the drafting component for sustainable andcontinuous operation. Drafting is accomplished by a stretching forcecreated due to the difference in speed between the last and immediatelyupstream pairs of rollers. According to the embodiment using three pairsof rollers, the second pair of rollers 19 rotates slower than the thirdpair of rollers 21 under appropriate pressure to prevent slipping.However, the overall draft ratio is calculated based on the ratio of thespeed of the last rollers versus the speed of the first rollers. Thepressure on each pair of rollers can be adjusted according to the typeof feeding fiber and the drafting ratio. In the present invention, thisis accomplished using different weight of pendulums and relativeposition of pendulums to the rollers. By varying the speed differenceand the pressure exerted by the pendulum, the apparatus is able toprocess different fibers with various tows as well as two or morefibers, of the same kinds or different types, simultaneously. In oneexemplary embodiment, the stretching is accomplished by a draft ratiobetween first roller pair 17 and second roller pair 19 to produce astretched material or a frayed ribbon (see FIGS. 6A-6C) which is asdescribed below as intermediate product 27 and is maintained generallyflat by passing between third roller pair 21 prior to being spun andtwisted in spinning component 13.

In another aspect of the present invention, apparatus 1 furthercomprises spinning component 13 as depicted in FIGS. 2, 4 and 5. Afterthe drafting procedure in drafting component 11, intermediate product 27exits the drafting component 11 and is directed to spinning component13. Intermediate product 27 is shown in detail in FIGS. 6B and 6C. Usingoptional spinning component 13, intermediate product 27 may be directlyspun into yarn 49 on bobbin 51 in one simple spinning and twistingoperation. By incorporating spinning component 13, the filament networkmay be directly processed into fine yarn with a yarn count of 1 to 60 Nmon the same apparatus and in one further operation. Yarns with otheryarn counts may be produced in other exemplary embodiments. The unit,“Nm”, is a measure of the thickness of yarn in term of the length inmeters for one gram of yarn. For instance, if one gram of yarn is 20meters in length, then the yarn count is 20 Nm. Therefore, the higherthe Nm, the thinner the yarns. In one aspect, the generally flatintermediate product 27 is spun and twisted into yarn 49 which isgenerally round in one simple spinning and twisting operation. In oneaspect, a small tow of oxidized PAN filaments of various tow sizes canbe formed into a cohesive elongated network of oxidized PAN fibers whichare then spun and twisted into yarns with about 10 to 28 Nm. In oneembodiment, the yarn is formed of 100% oxidized PAN fibers having lengthcharacteristics as described in conjunction with the intermediateproduct 27 as described herein. The process of the present invention canproduce very thin yarn in a simple, efficient and economical process.

Intermediate Product

The apparatus of the present invention can process a variety ofdifferent filamentous feed materials 15 as disclosed above and produce awool-like intermediate product 27 with distinct physical characteristicsfrom the feed material. Intermediate product 27 is characterized asbeing directly spinnable into yarn 49 and may be characterized as acohesive elongated network of fibers such as oxidized PAN fibers. Unlikethe well organized and aligned filaments of the precursor tow, thecontinuous and cohesive elongated network of fibers produced using thepresent invention may be a wool-like collection of random fibers withvery little parallel interactions between individual fibers and novisible twist between the individual fibers. The intermediate product27, i.e. the cohesive elongated network of fibers, may be composed offibers from a single starting material or intermediate product 27 mayalso be composed of fibers from several starting materials to form ablended continuous and cohesive fibrous network capable of being spuninto yarn in one further spinning step. The blended networks may beformed by drafting two or more different starting materials (filamentsor fibers) on the same apparatus simultaneously or by mixing theintermediate networks obtained individually. Intermediate product 27 canbe further processed into yarn with very small yarn count and withadditional enhanced properties and characteristics, such as increasedtensile strength.

Generally, an individual fiber of intermediate product 27 has a diameterof no greater than that of the original filament of the precursor fiberfrom which it was formed but may be a collection of individual filamentsbroken together and therefore having a greater diameter. Theintermediate product contains multiple short wavy fibers that arerandomly piled together. In one embodiment, the continuous and cohesivefibrous network is obtained from an aligned and continuous oxidized PANtow with no greater than 192K filaments. Preferably, the precursor towwill have no greater than 96K filaments. More preferably, the precursoris small filament tow with no more than about 48K, 24K, 12K, 6K or 3Kfilaments. In one embodiment, each fiber of the oxidized PAN network isno longer than about 40 cm in length.

In another embodiment, the fluffy continuous and cohesive fibrousnetwork may be obtained from an aligned and continuous stainless steeltow of no greater than 192K filaments. Preferably, the precursorstainless steel tow has no greater than about 192K filaments. Morepreferably, the precursor stainless steel tow has no greater than 192Kfilaments. Yet more preferably, the precursor stainless steel tow has nogreater than 12K filaments. Each fiber of the cohesive and continuousstainless steel fibrous network has a length of no greater than 40 cm.

In yet another embodiment, the fluffy filament network is obtained froman aligned and continuous aramid filamentous material with a tow of nogreater than 192K. Preferably, the precursor fiber has no greater than96K filaments. More preferably, the precursor has no greater than 48Kfilaments. Yet more preferably, the precursor fiber has no greater thanabout 12-24K filaments. Each filament of aramid network may have alength of no greater than 40 cm in one exemplary embodiment.

FIGS. 6A-C illustrate expanded views of feed material 15 and thecohesive elongated network of fibers, intermediate product 27. In FIG.6A, feed material 15 is in ribbon form and is formed of a plurality oflongitudinally aligned filaments. Feed material 15 has smooth surface 55and cross-section 57 is formed of cross-sections of the plurality offilaments that are relatively tightly packed and longitudinally aligned.Feed material 15 is an untwisted, flat form of starting material 7 andrepresents small filament tow such that the number of filaments that arelongitudinally aligned to form cross-section 57 may be in the range of3K, 6K, 12K, 24K and in other exemplary embodiments, the ribbon of towformed of a plurality of longitudinally aligned filaments may be largefilament tow, with the number of filaments in the 48K to 360K range.Each of the filaments are very long filaments which are a singlecontinuous strand of fibrous material as described above. FIG. 6A showsfilaments extending the length of the ribbon, i.e. feed material 15,with the filaments spaced apart for illustrative purposes only and itshould be understood that the filaments are aligned adjacent one anotherand extend throughout and across feed material 15, i.e. feed material 15and starting material 7 is formed entirely of the filaments that make upthe entire cross-section. In one exemplary embodiment width 58 may beabout 1.5 cm for 12K tow of oxidized PAN but other suitable dimensionsmay be used in other exemplary embodiments.

FIG. 6B shows the cohesive elongated network of fibers formed afterprocessing through the drafting operation in drafting component 11.Intermediate product 27 has a wool-like appearance, i.e., it is notsmooth but is rather crimped or scale-like and therefore surface 59 isnot a smooth surface. Intermediate product 27 is a cohesive andcontinuous fibrous network having an irregular surface and may bealternatively described as a network of a random collection of untwistedtruncated filaments that are held together by mechanical, physical andnoncovalent chemical forces. Intermediate product 27 is generally flat(not round) as shown in FIG. 6B but may have other appearances in otherexemplary embodiments. Width 60 will be generally the same as width 58of feed material 15 or it may vary slightly but feed material 15 andintermediate product 27 may have substantially the same generally flatconfiguration in one exemplary embodiment. Intermediate product 27 hasthe appearance of a frayed ribbon. Now turning to FIG. 6C, individualfibers 61 that are formed by separating the originally long filaments ofstarting material 7, are randomly arranged and wavy. Individual fiber 61may also be described as a truncated filament and may include a lengthranging from 2-9 inches in some exemplary embodiments and in oneexemplary embodiment, substantially all of the individual fibers 61 ofthe cohesive elongated network of fibers of intermediate product 27 maybe at least 15 centimeters long. In one exemplary embodiment,substantially all of the individual fibers 61 of the cohesive elongatednetwork of fibers of intermediate product 27 may be at least 10centimeters long. In another embodiment, a majority of individual fibers61 include a minimum length of 10 or 15 cm. In one exemplary embodiment,the average length of individual fibers 61 of the cohesive elongatednetwork of fibers may be at least 10 or 15 or 20 centimeters long. Inanother aspect, individual fibers 61 have a length within a range ofabout 2.5 cm to about 23 cm. In another embodiment 100% of the fibersare oxidized PAN fibers having a length within a range of about 15 cm toabout 23 cm. The length and distribution of lengths of fibers 61 enhancethe characteristics of yarn formed by spinning and twisting intermediateproduct 27 such that the yarn includes an increased knittabilitycompared to conventional yarns formed from oxidized PAN and may be moreeasily knitted, woven or crocheted into various fabrics. Thesecharacteristics are achievable without the addition of strengtheningfibers to the yarn or intermediate product such as required inconventional materials or using conventional methods.

In one aspect, the fire retardant and heat resistant yarn may include100% oxidized polyacrylonitrile (PAN) fibers in which the fibers have anaverage length greater than about 10 cm. The fibers may alternativelyhave an average length greater than about 15 cm. The fibers may eachhave a length within a range of about 2.5 cm to about 23 cm.

Post-Processing

The yarn produced from cohesive elongated network of fibers ofintermediate product 27 according to the present invention can befurther processed mechanically and/or chemically. The networks can bereadily spun into yarn using the aforementioned or other conventionalprocesses. The yarn formed of 100% oxidized PAN exhibits an increasedknittability without strengthening fibers compared to conventional yarnsformed from oxidized PAN. The yarn may be used in substantially anydesired fabricated form, woven or non-woven. The yarn can then be woven,stitched, braided, knitted, crocheted or formed into non-woven sheets,as well as other flat or three-dimensional shaped structures. Exemplaryproducts obtained through mechanical processing are herringbone weavecloth, twill weave tape, tubular woven fabric, paper, blankets, roving,yarn, cord, and rope. Filamentous materials can also be formed directlyinto sheets and other structures, either alone or in combination withother filaments, fibers, or compositions, such as resin.

The cohesive elongated network of fibers may also be treated chemicallyto impart new characteristics before or after being spun into yarns. Forexample, the cohesive elongated network of fibers may be fluorinated asdisclosed in U.S. Pat. No. 4,857,394 so as to provide flexible fiberswith different electrical conductivity. Another example is to convertoxidized PAN fibrous networks into carbon fibers by pyrolysis. Thisprocess involves two steps: carbonization and graphitization. During thecarbonization process, the oxidized PAN may be carbonized by stretchingand further heating to a temperature of about 1000 to 1500.degree. C. toremove non-carbon elements and form the carbonized PAN structurallyillustrated in FIG. 1. Carbonized PAN includes a higher carbon contentthan oxidized PAN and generally a carbon content of 90% or greater.Another aspect of the invention is the yarn described above anddownstream products formed from the yarn, but formed of PAN that hasbeen carbonized to carbonized PAN. During graphitization, the fiber isfurther treated at temperatures between about 1,500-3,000.degree. C. toimprove the ordering and orientation of the crystallites in thedirection of the fiber axis.

Applications

The cohesive elongated network of fibers and the yarns produced by theprocess of the present invention can be used as intermediates for theproduction of a range of industrial and consumer products. For example,oxidized PAN fibers are chemically resistant, thermally stable, andphysiologically harmless. The fibrous networks also have excellentprocessing properties such as superior blending and handingcharacteristics. They are ideally suited for heat resistant, thermal andacoustic insulation and technical textiles. The oxidized PAN fibrousnetworks can also be used as asbestos replacing additives in frictionlinings of automotive disc and drum brakes.

The oxidized PAN filaments and their downstream products such as yarnsand fabrics can be formed into consumer products and/or furtherprocessed under high temperatures into carbon fibers that have very highflame proof characteristics and are electrically conductive. Consumerproducts include various textiles such as blankets, jacket linings, bootlinings, helmet linings, jerseys, shirts, pants, balaclavas, and thelike.

Such carbon-fiber based materials are also useful in the production of avariety of industrial and consumer products, such as apparel and othertextile-based products, belts and hoses, composites, fiber optics,electromechanical materials, friction sensitive products such as gasketsand brake pads, tires, ropes and cables. The fibrous networks can alsobe processed into activated PAN fiber using various suitable knownmethods. This activated PAN product has very high surface area thus hashigh adsorption rate and capacity. It can be used to develop air filter,mask, water purification, odor adsorbing cloth, and protecting clothing.

In another embodiment, the PAN fibers and products may be impregnatedwith various suitable additives to impart various desired qualities.Such carbon-fiber based impregnated materials find various industrialapplications and are also useful in the production of a variety ofindustrial and consumer products, such as apparel and othertextile-based products, belts and hoses, composites, fiber optics,electromechanical materials, friction sensitive products such as gasketsand brake pads, tires, ropes and cables, filtration systems such as airfilters, masks, water purification systems, odor adsorbing cloth, andother protecting clothing.

Fabrics formed from oxidized or further processed PAN such as carbonizedPAN and activated PAN formed according to the invention exhibit superiortensile strength and knittability compared to fabrics of 100% PAN formedusing conventional methods, which require the addition of strengtheningfibers or encapsulation to function as viable textiles or fabrics. Anaspect of the invention is the production of oxidized, carbonized oractivated PAN fabrics and other textiles formed from yarn producedaccording to the invention without the use of strengthening fibers orwithout encapsulating the formed fabrics.

The materials of the invention may be used in various applications toproduce products such as fire-resistant clothing, thermal insulation andindustrial filters, heat shields for automotive disk brakes, electricalinsulation such as papers and pressboards and high-temperaturefiltration applications for pollution control. The products may be usedin other applications ranging from aircraft and railroad car interiortextiles (including upholstery, floor coverings, bulkheads and wallcoverings) to contract furnishings for hotels, offices, auditoriums,hospitals and day care centers. The products in the wide range ofapplications may be produced using various manufacturing methods knownin the art.

EXAMPLES

The following are examples of methods for producing the inventivecohesive elongated network of fibers and yarns are intended to beexemplary and not restrictive of the methods, apparatus configurationsand products of the invention. The exemplary apparatus for each of thefollowing examples had either two or three pairs of rollers as indicatedin each example. All of the rollers attached to the apparatus had thesame diameter of 31.84 mm. All of the rollers attached to the pendulumhad cots with the same hardness of 75 according to the Shore A hardnessscale.

Example I

Oxidized PAN Fiber Network Produced from a Tow of 6K Filaments

The precursor material is an oxidized PAN with a tow size of 6K, a towdenier of 7,200, and tow weight of 0.8 g/mlter. Its general physicalproperties are summarized in Table 1. The precursor material containsparallel filaments of a uniform length equal to the length of tow, whichoften exceeds 2 meters. The filament is also well organized and alignedlongitudinally. Additionally, the precursor fiber has very limitedtwists, typically less than 5 turns per meter. The oxidized PAN fiberwas drafted using the apparatus with two pairs of rollers, the firstrollers and last rollers. The distance between two rollers attached tothe apparatus was set to about 240 mm. To obtain a draft ratio of 27.2,the speeds of the last and preceding rollers were set at 227 and 8.3rpm, respectively. The same pressure was applied to both pairs ofrollers. The pressure was adjusted to about 28 Kg by varying the weighton the pendulum carrier. The drafting process broke and randomized thelong and organized filaments of the precursor fiber to form a fluffy webwhich has very little parallel interactions between the individualfibers formed by breaking and stretching the filaments, and no visibletwist between the individual fibers. The fibers of the cohesiveelongated network of fibers appear wavy and have lengths no greater thanabout 22 cm and a width of no greater than 12 micrometers. The networkhas an average weight of about 0.077 g/10 cm. TABLE-US-00001 TABLE 1Physical Properties Data Filament denier 1.2 denier Density 1.40g/cm.sup.3 Single filament diameter 11 micrometer Tensile strength 2.0g/denier Elastic modulus 450 Kg/mm.sup.2 Moisture regain 9% Strength atbreak 14 CN/tex Elongation at break 10% LOI 55

The cohesive elongated network of fibers was further processed bywinding and twisting in one operation to yield a yarn with a yarn countof 34 Nm, a tensile strength of 250-300 g, a tensile elongation of 10%,and a twist count of 525 (T/meter).

Example II

Oxidized PAN Network Produced from a Filamentous Starting Material witha 12K Tow

The precursor material is an oxidized PAN with a tow size of 12K, a towdenier of 14,400, and tow weight of 1.6 g/mlter. Its general physicalproperties are summarized in Table 1. The precursor material containsparallel filaments of a uniform length equal to the length of tow, whichoften exceeds 2 meters. Additionally, the filaments of the precursormaterial has very limited twists, typically less than 5 turns per meter.The oxidized PAN was drafted using the apparatus having only first andlast pairs of rollers. The distance between the rollers attached to theapparatus was set to about 240 mm. To obtain a draft ratio of 8, thespeeds of the first and last rollers were set at 125 and 15.6 rpm,respectively. The pressures applied onto the first and last rollers were45 and 50 Kg, respectively. The pressure was adjusted by varying theweight on the pendulum carrier and the position of the pendulum on thependulum carrier. The drafting process broke and randomized the long andorganized filaments of the precursor fiber to form a wool-like networkof truncated filaments, with very little parallel interactions betweenindividual fibers and has no visible twists between individualfilaments. The fibers of the network formed by separating the originalfilaments appear wavy and have a length of no greater than about 22 cmand a width of no greater than about 12 micrometers. The network has anaverage weight of about 0.159 g/10 cm.

The cohesive elongated network of fibers was further processed bywinding and twisting to yield a yarn with a yarn count of 5 Nm, atensile strength of about 2000 g, a tensile elongation of 10%, and atwist count of 100 (T/meter).

Example III

An Oxidized PAN Network Produced from Two Feeding Materials

This example illustrates the drafting of two fibers of the same typesimultaneously. However, the drafting process is equally applicable totwo or more fibers of different kinds. The two incoming materials werefed using a feeding component as depicted in FIG. 1. The two precursorfibers are oxidized PAN with a tow size of 6K, a tow denier of 7,200,and tow weight of 0.8 g/mlter. Their general physical properties aresummarized in Table 1. The precursor contains parallel filaments of auniform length equal to the length of tow, which often exceeds 2 meters.The filaments are also well organized and aligned longitudinally.Additionally, the precursor fiber has very limited twists, typicallyless than 5 turns per meter. The oxidized PAN fibers were drafted usingthe apparatus with two pairs of rollers. The distance between the tworollers attached to the apparatus was set to about 240 mm. To obtain adraft ratio of 27.2, the speeds of the rollers were set at 227 and 8.3rpm, respectively. The same pressure was applied to both pairs ofrollers. The pressure was adjusted to about 28 Kg by varying the weightof a pendulum on the pendulum carrier. The drafting process broke andrandomized the long and organized filaments of the precursor fibers toproduce a wool-like fibrous network which has very little parallelinteractions between individual fibers and has no visible twist betweenthe individual fibers. The fibers of the network appear wavy and havelengths of about no greater than about 22 cm and a width of no greaterthan about 12 micrometers. The network has average weight of about 0.154g/10 cm.

The cohesive elongated network of fibers was further processed bywinding and twisting to yield a yarn with a yarn count of 17 Nm, atensile strength of about 500-600 g, a tensile elongation of about 10%,and a twist count of about 375 (T/meter).

Example IV A Stainless Steel Fibrous Network

The precursor is a stainless steel fiber with a tow size of 4K, and towweight of 1.6 g/mlter. In addition to its major chemical element, iron(Fe), the steel also contains several other elements as listed in Table2.

The precursor fiber contains parallel filaments of a uniform lengthequal to the length of tow, which often exceeds 2 meters. The filamentsare also well organized and aligned longitudinally. Additionally, thefilaments of the precursor material has very limited twists, typicallyless than 5 turns per meter. The filament has a tenacity strength of 7.5CN and a diameter of 8 micrometer. The stainless steel incoming materialwas drafted using the apparatus with three pairs of rollers. Thedistance between the first and second rollers attached to the apparatuswas set to be 100 mm whereas the distance between the second and thethird rollers attached to the apparatus was set to be 140 mm. To obtaina draft ratio of 17.6, the speeds of the first, second and third rollerswere set at 200, 11.4, and 10.8 rpm, respectively. The same pressure wasapplied to the first and second rollers and was set at 42 Kg. Thepressure applied onto the first rollers was set at 45 Kg. Similar to theprevious examples, the pressure was adjusted by varying the weight ofthe pendulum and the position of the pendulum on the pendulum carrier.The drafting process broke and randomized the long and organizedfilaments of the precursor to form a wool-like fiber network having verylittle parallel interactions between individual fibers and has novisible twist between the individual fibers. The fibers of the networkformed from the incoming filaments appear wavy and have a length of nogreater than about 10 cm and a width of about 8 micrometers. The networkhas an average weight of about 0.16 g/10 cm. TABLE-US-00002 TABLE 2Chemical Compositions Percent (%) C 0.03 Si 1.0 Mn 2.0 Ni 10.0-14.0 Cr16.0-18.0

The filament network was further processed by winding and twisting toyield a yarn with a yarn count of 11 Nm and a twist count of 500(T/meter).

Example V

Aramid Filament Network Produced from a 1K Tow Aramid Starting material

The precursor feed material is an aramid material with a tow size of 1K,a tow denier of 1,530, and tow weight of 0.17 g/mlter. Its generalphysical properties are summarized in Table 3. The precursor containsparallel filaments of a uniform length equal to the length of tow, whichoften exceeds 2 meters. The filaments are also well organized andaligned longitudinally and have a diameter of 12 micrometers.Additionally, the precursor filaments have very limited twists,typically less than 5 turns per meter. The aramid material was draftedusing the apparatus with two pairs of rollers, the first and lastrollers. The distance between the first and last rollers mounted on theapparatus was about 240 mm. To obtain a draft ratio of 8.5, the speedsof the first and last rollers were set at 170 and 10 rpm, respectively.The pressures applied onto the first and last rollers were above about42 and 45 Kg, respectively. The pressure was adjusted by varying theweight of the pendulum and the position on the pendulum carrier. Theprecursor aramid material was drafted twice. The first drafting resultedin a stretching of the filaments. The second drafting broke andrandomized the long and organized filaments of the precursor to form awool-like fiber network which has very little parallel interactionsbetween individual fibers and has no visible twist between theindividual fibers. The fibers of the network appear wavy and have alength of no greater than about 22 cm and a width of about 12micrometers. The network has an average weight of about 0.015 g/10 cm.TABLE-US-00003 TABLE 3 Physical Properties Data Filament denier 1.53denier Tenacity 23 g/denier Tensile strength 3,000 N/mm.sup.2 Tensilemodulus 67 kN/mm.sup.2 Elongation at break 3% Filament diameter 12micrometer Density 1.38 g/cm.sup.3 Decomposition point 500 LOI 29

The cohesive elongated network of fibers was further processed bywinding and twisting to produce a yarn with a yarn count of 50 Nm and atwist count of 800 T/meter.

The preceding merely illustrates the principles of the invention. Itwill thus be appreciated that those skilled in the art will be able todevise various arrangements which, although not explicitly described orshown herein, embody the principles of the invention and are includedwithin its spirit and scope. Furthermore, all examples and conditionallanguage recited herein are principally intended expressly to be onlyfor pedagogical purposes and to aid the reader in understanding theprinciples of the invention and the concepts contributed by theinventors to furthering the art, and are to be construed as beingwithout limitation to such specifically recited examples and conditions.Moreover, all statements herein reciting principles, aspects, andembodiments of the invention, as well as specific examples thereof, areintended to encompass both structural and functional equivalentsthereof. Additionally, it is intended that such equivalents include bothcurrently known equivalents and equivalents developed in the future,i.e., any elements developed that perform the same function, regardlessof structure.

This description of the exemplary embodiments is intended to be read inconnection with the figures of the accompanying drawing, which are to beconsidered part of the entire written description. In the description,relative terms such as “lower,” “upper,” “horizontal,” “vertical,”“above,” “below,” “up,” “down,” “top” and “bottom” as well asderivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,”etc.) should be construed to refer to the orientation as then describedor as shown in the drawing under discussion. These relative terms arefor convenience of description and do not require that the apparatus beconstructed or operated in a particular orientation. Terms concerningattachments, coupling and the like, such as “connected” and“interconnected,” refer to a relationship wherein structures are securedor attached to one another either directly or indirectly throughintervening structures, as well as both movable or rigid attachments orrelationships, unless expressly described otherwise.

All patents, publications, scientific articles, web sites, and otherdocuments and materials referenced or mentioned herein are indicative ofthe levels of skill of those skilled in the art to which the inventionpertains, and each such referenced document and material is herebyincorporated by reference to the same extent as if it had beenincorporated by reference in its entirety individually or set forthherein in its entirety. Applicants reserve the right to physicallyincorporate into this specification any and all materials andinformation from any such patents, publications, scientific articles,web sites, electronically available information, and other referencedmaterials or documents.

The written description portion of this patent includes all claims.Furthermore, all claims, including all original claims as well as allclaims from any and all priority documents, are hereby incorporated byreference in their entirety into the written description portion of thespecification, and Applicants reserve the right to physicallyincorporate into the written description or any other portion of theapplication, any and all such claims. Thus, for example, under nocircumstances may the patent be interpreted as allegedly not providing awritten description for a claim on the assertion that the precisewording of the claim is not set forth in haec verba in writtendescription portion of the patent.

The claims will be interpreted according to law. However, andnotwithstanding the alleged or perceived ease or difficulty ofinterpreting any claim or portion thereof, under no circumstances mayany adjustment or amendment of a claim or any portion thereof duringprosecution of the application or applications leading to this patent beinterpreted as having forfeited any right to any and all equivalentsthereof that do not form a part of the prior art.

All of the features disclosed in this specification may be combined inany combination. Thus, unless expressly stated otherwise, each featuredisclosed is only an example of a generic series of equivalent orsimilar features.

It is to be understood that while the invention has been described inconjunction with the detailed description thereof, the foregoingdescription is intended to illustrate and not limit the scope of theinvention, which is defined by the scope of the appended claims. Thus,from the foregoing, it will be appreciated that, although specificembodiments of the invention have been described herein for the purposeof illustration, various modifications may be made without deviatingfrom the spirit and scope of the invention. Other aspects, advantages,and modifications are within the scope of the following claims and thepresent invention is not limited except as by the appended claims.

The specific methods and compositions described herein arerepresentative of preferred embodiments and are exemplary and notintended as limitations on the scope of the invention. Other objects,aspects, and embodiments will occur to those skilled in the art uponconsideration of this specification, and are encompassed within thespirit of the invention as defined by the scope of the claims. It willbe readily apparent to one skilled in the art that varying substitutionsand modifications may be made to the invention disclosed herein withoutdeparting from the scope and spirit of the invention. The inventionillustratively described herein suitably may be practiced in the absenceof any element or elements, or limitation or limitations, which is notspecifically disclosed herein as essential. Thus, for example, in eachinstance herein, in embodiments or examples of the present invention,the terms “comprising”, “including”, “containing”, etc. are to be readexpansively and without limitation. The methods and processesillustratively described herein suitably may be practiced in differingorders of steps, and that they are not necessarily restricted to theorders of steps indicated herein or in the claims.

The terms and expressions that have been employed are used as terms ofdescription and not of limitation, and there is no intent in the use ofsuch terms and expressions to exclude any equivalent of the featuresshown and described or portions thereof, but it is recognized thatvarious modifications are possible within the scope of the invention asclaimed. Thus, it will be understood that although the present inventionhas been specifically disclosed by various embodiments and/or preferredembodiments and optional features, any and all modifications andvariations of the concepts herein disclosed that may be resorted to bythose skilled in the art are considered to be within the scope of thisinvention as defined by the appended claims.

The invention has been described broadly and generically herein. Each ofthe narrower species and subgeneric groupings falling within the genericdisclosure also form part of the invention. This includes the genericdescription of the invention with a proviso or negative limitationremoving any subject matter from the genus, regardless of whether or notthe excised material is specifically recited herein.

It is also to be understood that as used herein and in the appendedclaims, the singular forms “a,” “an,” and “the” include plural referenceunless the context clearly dictates otherwise, the term “X and/or Y”means “X” or “Y” or both “X” and “Y”, and the letter “s” following anoun designates both the plural and singular forms of that noun. Inaddition, where features or aspects of the invention are described interms of Markush groups, it is intended, and those skilled in the artwill recognize, that the invention embraces and is also therebydescribed in terms of any individual member or subgroup of members ofthe Markush group.

Other embodiments are within the following claims. The patent may not beinterpreted to be limited to the specific examples or embodiments ormethods specifically and/or expressly disclosed herein. Under nocircumstances may the patent be interpreted to be limited by anystatement made by any Examiner or any other official or employee of thePatent and Trademark Office unless such statement is specifically andwithout qualification or reservation expressly adopted in a responsivewriting by Applicants.

Although the invention has been described in terms of exemplaryembodiments, it is not limited thereto. Rather, the appended claimsshould be construed broadly, to include other variants and embodimentsof the invention, which may be made by those skilled in the art withoutdeparting from the scope and range of equivalents of the invention.

1. A fire retardant and heat resistant yarn consisting essentially of100% oxidized polyacrylonitrile (PAN) fibers, said fibers having anaverage length greater than about 10 cm, substantially all of saidfibers having a length within a range of about 2.5 cm to about 23 cm. 2.The fire retardant and heat resistant yarn as in claim 1, wherein saidoxidized PAN fibers have an average length greater than about 15 cm. 3.A fabric consisting essentially of yarn formed of a plurality of fireretardant and heat resistant fibers and no strengthening fibers, each ofsaid fire retardant and heat resistant fibers comprising 100%polyacrylonitrile (PAN), said fibers having an average length greaterthan about 10 cm, a majority of said fibers having a length within arange of about 2.5 cm to about 23 cm, said PAN being one of oxidized PANand carbonized PAN.
 4. The fabric as in claim 3, wherein said PANcomprises oxidized PAN and said fabric comprises wearing apparel.
 5. Thefabric as in claim 3, wherein said PAN comprises oxidized PAN and saidfabric comprises one of a jersey, a jacket lining, a boot lining, ahelmet lining and a blanket.
 6. The fabric as in claim 3 wherein saidPAN comprises carbonized PAN.
 7. A fire retardant and heat resistantyarn consisting essentially of 100% carbonized polyacrylonitrile (PAN)fibers, said fibers having an average length greater than about 15 cm,substantially all of said fibers having a length within a range of about2.5 cm to about 23 cm.
 8. An unencapsulated fabric consistingessentially of yarn formed of a plurality of fire retardant and heatresistant fibers and no strengthening fibers, each of said fireretardant and heat resistant fibers comprising 100% polyacrylonitrile(PAN).
 9. The unencapsulated fabric as in claim 8, wherein said PANcomprises oxidized PAN and said fabric comprises one of a jersey, ajacket lining, a boot lining, a helmet lining and a blanket.
 10. Theunencapsulated fabric as in claim 8, wherein said PAN comprisescarbonized PAN and said fabric comprises one of a jersey, a jacketlining, a boot lining, a helmet lining and a blanket.
 11. Theunencapsulated fabric as in claim 8, wherein said PAN comprisesactivated and carbonized PAN and said fabric comprises one of a jersey,a jacket lining, a boot lining, a helmet lining and a blanket.
 12. Afire retardant and heat resistant strand of material consisting of 100%oxidized polyacrylonitrile (PAN) fibers, said fire retardant and heatresistant strand formed according to the method of: providing a startingmaterial comprising a tow of filaments forming a ribbon; drawing saidstarting material through a first pair of rollers and a seconddownstream pair of rollers of a drafting component while urging saidfirst pair of rollers toward each other and said second pair of rollerstoward each other, said second pair of rollers having a secondrotational speed that is faster than a first rotational speed of saidfirst pair of rollers, thereby stretching and breaking said filaments ofsaid tow of filaments to form a cohesive elongated network of fibersformed by said stretching and breaking said filaments.
 13. The fireretardant and heat resistant strand of material as in claim 12, whereinsaid cohesive elongated network of fibers is wool-like, generally flatand said fibers are wavy and randomly oriented within said cohesiveelongated network of fibers.
 14. The fire retardant and heat resistantstrand of material as in claim 12, wherein said fibers have an averagelength greater than about 15 cm, each said fiber having a length withina range of about 2.5 cm to about 23 cm.
 15. A fire retardant and heatresistant yarn consisting of 100% oxidized polyacrylonitrile (PAN)fibers, said fire retardant and heat resistant yarn formed according tothe method of: providing a starting material comprising a plurality oflongitudinally aligned oxidized PAN filaments with limited twists;converting said starting material into a fire retardant and heatresistant cohesive elongated network of fibers in a single operationthat stretches and breaks said filaments of said starting material,thereby separating at least some of said filaments into a plurality ofsaid fibers having lengths shorter than said corresponding filamentsfrom which said fibers were separated; and directly spinning saidcohesive elongated network of fibers into yarn in one spinning step thatfurther twists said cohesive elongated network of fibers.
 16. The fireretardant and heat resistant yarn as in claim 15, wherein said cohesiveelongated network of fibers is wool-like and said fibers are wavy andrandomly oriented within said cohesive elongated network of fibers. 17.The fire retardant and heat resistant yarn as in claim 15, wherein saidfibers having an average length greater than about 10 cm, substantiallyall of said fibers having a length within a range of about 2.5 cm toabout 23 cm.
 18. The fire retardant and heat resistant yarn as in claim15, wherein said starting material comprises a ribbon of small filamenttow with no greater than 24K filaments and said method further comprisesmaintaining said ribbon flat and untwisted until said converting.